CLONING AND CHARACTERIZATION OF LUNG ENDOTHELIAL-CELL ADHESION MOLECULE-1 SUGGEST IT IS AN ENDOTHELIAL CHLORIDE CHANNEL

Lung-endothelial cell adhesion molecule-1 (Lu-ECAM-1) is an endothelia l cell surface molecule that mediates adhesion of metastatic melanoma cells to lung endothelium, Here we analyze the organization of the Lu- ECAM-1 protein complex, report the sequence of Lu-ECAM-1 cDNAs, and re veal a novel function of the protein, Lu-ECAM-1 immunopurified from bo vine aortic endothelial cells (BAEC) consists of tightly associated gl ycoproteins of 90, 38, and 32 kDa, with minor components of 130 and 12 0 kDa, We present evidence that all of these protein species are encod ed by a single open reading frame whose initial translation product is proteolytically processed to yield the other products, Correct proces sing in. vitro was demonstrated by transfection of the longest cDNA in to human embryonic kidney 293 cells; immunoblot analysis showed that t he similar to 120-kDa precursor gave rise to 90- and 38-kDa products, RNA blots of BAEC mRNA detected messages in agreement with the sizes o f the cDNA clones in addition to several of high molecular weight, DNA blot analysis showed that Lu-ECAM-1 is conserved throughout its lengt h in all mammals tested, usually as a single or low copy gene, In the bovine, Lu-ECAM-1 protein is 88% identical to a calcium-dependent chlo ride channel described recently in tracheal epithelium, Ca-CC, Probes for Lu-ECAM-1 mRNA and protein confirmed the presence of a homolog in this tissue, We show that messages for both proteins are present in lu ng while only Ca-CC is present in trachea and only Lu-ECAM-1 is presen t in BAEC, These results suggest that endothelial cells express a chlo ride channel that is related to, but distinct from, that expressed in tracheal epithelium, They further suggest that an adhesion molecule ca n also be a chloride channel.